1. Field of the Invention
The present invention relates to hearing aids. The invention, more specifically, relates to an earpiece for a hearing aid adapted for increasing the hearing aid output in at least one frequency range. The invention further relates to a method of making such an earpiece for a hearing aid.
In the context of the present disclosure, a hearing aid should be understood as a small, battery-powered, microelectronic device designed to be worn behind or in the human ear by a hearing-impaired user. Prior to use, the hearing aid is adjusted by a hearing aid fitter according to a prescription. The prescription is based on a hearing test, resulting in a so-called audiogram, of the performance of the hearing-impaired user's unaided hearing. The prescription is developed to reach a setting where the hearing aid will alleviate a hearing loss by amplifying sound at frequencies in those parts of the audible frequency range where the user suffers a hearing deficit. A hearing aid comprises one or more microphones, a battery, a microelectronic circuit comprising a signal processor, and an acoustic output transducer. The signal processor is preferably a digital signal processor. The hearing aid is enclosed in a casing suitable for fitting behind or in a human ear.
As the name suggests, Behind-The-Ear (BTE) hearing aids are worn behind the ear. To be more precise an electronics unit comprising a housing containing the major electronics parts thereof is worn behind the ear. An earpiece for emitting sound to the hearing aid user is worn in the ear, e.g. in the concha or the ear canal. In a traditional BTE hearing aid, a sound tube is used because the output transducer, which in hearing aid terminology is normally referred to as the receiver, is located in the housing of the electronics unit. In some modern types of hearing aids a conducting member comprising electrical conductors is used, because the receiver is placed in the earpiece in the ear. Such hearing aids are commonly referred to as Receiver-In-The-Ear (RITE) hearing aids. In a specific type of RITE hearing aids the receiver is placed inside the ear canal. This is known as Receiver-In-Canal (RIC) hearing aids.
In-The-Ear (ITE) hearing aids are designed for arrangement in the ear, normally in the funnel-shaped outer part of the ear canal. This type of hearing aid requires a very compact design in order to allow it partly to be arranged in the ear canal, partly to house the components necessary for operation of the hearing aid, such as microphones, a battery, a microelectronic circuit comprising a signal processor, and an acoustic output transducer.
2. The Prior Art
DE-AS-1274658 discloses a receiver and a corresponding elastic casing, wherein the receiver sound output and the casing sound output are separated from each other, and a sound conduit between the two sound outputs are formed between the outer surface of the receiver housing and the inner surface of the corresponding elastic casing. Hereby the sound conduit is claimed to have sufficient length for increasing the low frequencies.
One problem with this system is that the sound conduit must run along the outer surface of the receiver housing. Therefore it is not possible to physically separate the receiver housing from the sound conduit. For some RITE hearing aids it is advantageous to have the receiver positioned in the concha or similar part of the external ear, and the main part of the sound conduit positioned in the ear canal. Obviously this is especially advantageous when the receiver is too large to be positioned in the ear canal.
U.S. Pat. No. 3,170,046 discloses an ITE hearing aid with an electroformed metal housing. Inside the metal housing the transmission of sound is conveyed by a sound tube, that connects the receiver and the terminal end of the metal housing located in the ear canal. The sound tube is preferably made of thin-walled natural rubber or similar materials such as polyethylene or vinyl. It is further disclosed that the reduction of acoustic feedback may be improved by providing a tortuous path for the sound tube.
EP-A1-1629806 discloses a hearing protection earplug with a resonance cavity, which is provided with an inner mechanical structure. For hearing protection devices it is desirable to provide for sufficient attenuation of undesired sound signals, such as noise, while preserving a more or less natural hearing impression for desired sound signals, such as natural speech, in order to enable speech communication in noisy environments. In other words, it would be desirable to have more or less frequency independent attenuation in order to achieve a close to natural hearing impression. In this respect it is important to note that the outer ear and the ear canal of a person have an individual natural resonance around 2.5 kHz to 3 kHz so that natural speech for which significant information is carried in this frequency region is selected over other sound signals such as noise. Any earplug worn in the ear canal will disturb this natural frequency of the ear canal. This problem is addressed by compensating the shortening of the ear canal by the earplug by correspondingly increasing the effective acoustic length within the earplug. In other words, if the cavity of the earplug is dimensioned such that the ear canal is effectively cut in two equal parts, the cavity of the earplug would be designed such that the effective acoustic length within the cavity is about double the geometrical length of the cavity.
However, despite the advanced technology level in current hearing aids some hearing impaired require a hearing aid output that is not easily achieved with the current technology. A significant part of the hearing impaired that require a very high hearing aid output will benefit especially from a very high output around 1 kHz.
It may be difficult for RITE, RIC or ITE hearing aids to provide a very high output around 1 kHz.
It is therefore a feature of the present invention to overcome at least these drawbacks and provide hearing aid earpieces and hearing aids that are easy to manufacture and optimized for hearing impaired users that require a high output around 1 kHz.
It is another feature of the current invention to provide a method for manufacturing a hearing aid earpiece according to the invention.